The disclosure of Japanese Patent Application No. 2002-085706 filed on Mar. 26, 2002 including the specification, drawings and abstract incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an art for estimating a tire condition amount in a vehicle, in particular, it relates to an art for estimating the tire condition amount based upon a rotational speed of that tire.
2. Description of Related Art
An art that estimates tire condition amounts such as tire pressure for purposes including the discovery of tire abnormalities in a vehicle while the vehicle is running already exists.
In an example of this art, a wheel speed sensor is fixed to a vehicle body side and used to detect a vehicle wheel speed of a vehicle wheel consisting of a tire fixed to a disc wheel. A tire condition amount is estimated by the wheel speed sensor.
More specifically, a reflected value that reflects the tire condition amount based upon the vehicle wheel speed detected by the wheel speed sensor is obtained, and the tire condition amount is estimated based upon the obtained reflected value.
As specific systems that estimate tire pressure as a tire condition amount, a dynamic load tire radius system and a tire vibration system are known.
In addition, a resonance frequency system, a disturbance observer system and the like are known tire vibration systems. In a case where the resonance frequency system is employed, the tire resonance phenomenon does not appear as conspicuously within a high speed region where a vehicle wheel speed or a vehicle speed is high, as in a low speed region.
Therefore, in Japanese Patent Laid-Open Publication No. 10-129222, the following type of art is disclosed for obtaining a resonance frequency of a rear vehicle wheel not only in a condition where the vehicle speed is in a low speed region, i.e. a condition where the resonance frequency detected for the rear vehicle wheel does not reach a detection limit, but also in a condition where the vehicle speed is in a high speed region, i.e. a condition where the resonance frequency detected for the rear vehicle wheel has reached a detection limit.
In that art, the resonance frequency of each vehicle wheel and the dynamic load radius reflected value that reflects a dynamic load radial difference between a front vehicle wheel and a rear vehicle wheel is used to determine the presence of abnormalities in the tire pressure condition.
Specifically, when the resonance frequency of the rear vehicle wheel does not exceed the detection limit, the resonance frequency of the rear vehicle wheel is detected, and the presence of abnormalities in the rear wheel tire pressure condition is determined based upon the detected resonance frequency.
On the contrary, when the resonance frequency of the rear vehicle wheel exceeds a detection limit, the resonance frequency of the rear vehicle wheel is estimated based upon the dynamic load radius reflected value at that time, and a previously detected resonance frequency for the rear vehicle wheel during a state in which the detection limit of the resonance frequency regarding the rear vehicle wheel was not exceeded.
Thus, according to the art disclosed in Japanese Patent Laid-Open Publication No. 10-129222, the resonance frequency of the rear vehicle wheel after exceeding the detection limit is estimated based upon the rear wheel resonance frequency prior to exceeding the detection limit, and the dynamic load radius reflected value after exceeding the detection limit.
Therefore, in this art, to estimate the rear wheel resonance frequency during an estimating period after the detection limit has been exceeded, an obtained resonance frequency for any one of the vehicle wheels cannot be used in a period corresponding to the estimating period.
Namely, according to this art, the resonance frequency detected before the estimating period is used in order to estimate the resonance frequency of the rear vehicle wheel in an estimating period after the detection limit has been exceeded.
Furthermore, according to this art, data obtained during a period corresponding to the estimating period is also used in order to estimate the resonance frequency of the rear vehicle wheel in an estimating period after the detection limit has been exceeded; that data is the dynamic load radius reflected value.
The physical type of the dynamic load radius reflected value is different from that of the resonance frequency that needs to be estimated for the rear vehicle wheel. Therefore, mutual conversion therebetween is necessary.
Also, since the dynamic load radius reflected value is generally obtained as one value representing all vehicle wheels in the vehicle, it is a physical amount with which it is difficult to reflect the tire pressure condition of each tire independent from the other tires.
Therefore, with this art there is a limit to improving the accuracy of estimating the resonance frequency of the rear vehicle wheel after the detection limit has been exceeded.
In other words, with this art it is difficult to accurately obtain a reflected value that reflects a tire condition amount of a vehicle wheel for which it is difficult to accurately obtain the reflected value among plural vehicle wheels in a vehicle.
It is an object of the invention to accurately obtain using other data, a reflected value that reflects a tire condition amount of a vehicle wheel for which is it difficult to accurately obtain the reflected value among plural vehicle wheels in a vehicle.
A first aspect of the invention relates to an apparatus that estimates the tire condition amount of each vehicle wheel, and is provided in a vehicle equipped with vehicle wheels formed with air enclosed under pressure in an inside portion of a tire mounted to a disc wheel. The apparatus includes a plurality of wheel speed sensors which detect a vehicle wheel speed of each vehicle wheel, a respective one of the sensors being provided in relation to a respective one of the plurality of vehicle wheels, and an estimating unit that obtains a reflected value reflecting a tire condition amount of each of the plurality of vehicle wheels based upon the vehicle wheel speed detected by each of the plurality of wheel speed sensors, and estimates the tire condition amount of each of the plurality of vehicle wheels based upon the obtained reflected value. The estimating unit estimates a reflected value of a first vehicle wheel for which it is relatively difficult to accurately obtain the reflected value based upon a vehicle wheel speed of the first vehicle wheel among the plurality of vehicle wheels, during a first period corresponding to a second period for obtaining the reflected value of the first vehicle wheel, based upon a reflected value obtained for a second vehicle wheel for which it is relatively easy to accurately obtain the reflected value based upon the vehicle wheel speed of the second vehicle wheel, in order to obtain the reflected value of the first vehicle wheel.
In the art disclosed in Japanese Patent Laid-Open Publication No. 10-129222 mentioned above, a resonance frequency of a rear vehicle wheel that is the first vehicle wheel, for which it is difficult to accurately obtain the reflected value that reflects the tire condition amount based upon the vehicle wheel speed, is estimated before the obtaining period using an obtained resonance frequency of a front vehicle wheel that is the second vehicle wheel, for which it is easier to accurately obtain the reflected value that reflects the tire condition amount based upon the vehicle wheel speed.
Therefore, in the art of Japanese Patent Laid-Open Publication No. 10-129222, the resonance frequency of the rear vehicle wheel cannot be estimated using the resonance frequency of the front vehicle wheel obtained during a period corresponding to the period when the resonance frequency of the rear vehicle wheel needs to be obtained.
Meanwhile, knowledge acquired through the research of the inventors of the invention indicated that under given conditions, a specific relationship is established at a mutually corresponding time between the first vehicle wheel and the second vehicle wheel in relation to the reflected value, and it is possible to obtain that specific relationship prior to use of the vehicle by a user.
The specific relationship is, for example, easily affected by the vehicle wheel load that perpendicularly acts on each vehicle wheel from the vehicle body, and a suspension characteristic connecting each vehicle wheel to the vehicle body. However, as long as the tire type of each vehicle wheel is replaced within the permissible range, it is hardly affected by the tire type. In other words, that specific relationship is minimally dependent on the tire type of each vehicle wheel.
Based upon the above described knowledge, in the apparatus according to the first aspect of the invention, the reflected value of the first vehicle wheel is estimated using the reflected value obtained for the second vehicle wheel in a period corresponding to the obtaining period thereof.
Therefore, according to this device, unlike the art of Japanese Patent Laid-Open Publication No. 10-129222, the reflected value of the first vehicle wheel can be estimated using the reflected value obtained for the second vehicle wheel in a period corresponding to a period when the reflected value of the first vehicle wheel needs to be obtained, thus enabling easy improvement of estimation accuracy of the reflected value of the first vehicle wheel.
In the first aspect of the invention, xe2x80x9cestimating a tire condition amountxe2x80x9d can be interpreted to signify estimating an absolute value of the tire condition amount, estimating a relative value (i.e. amount of variation) with respect to a threshold value of the tire condition amount, and estimating whether the tire condition amount is large or small with respect to a threshold value; i.e. determining the size of the tire condition amount.
In the invention, xe2x80x9cperiod corresponding to an obtaining periodxe2x80x9d, e.g., a first period corresponding to a second period for obtaining the reflected value, can be interpreted to signify a period completely identical to the obtaining period, a period that is virtually identical to the obtaining period, and a period whose difference from the obtaining period is within a set range.
A second aspect of the invention relates to an apparatus that estimates a tire condition amount of a vehicle wheel and is provided on a vehicle equipped with vehicle wheels formed with air enclosed under pressure in an inside portion of a tire mounted to a disc wheel. The apparatus includes a wheel speed sensor that detects a vehicle wheel speed of the vehicle wheel, and an estimating unit that, based on the vehicle wheel speed detected by the wheel speed sensor, obtains a reflected value reflecting a tire condition amount of the vehicle wheel and estimates the tire condition amount based upon the obtained reflected value. The estimating unit determines that there is a high probability that the tire condition amount of the vehicle wheel is normal if it is relatively difficult to accurately obtain the reflected value based upon the detected vehicle wheel speed, and determines that there is a high probability that the tire condition amount of the vehicle wheel is abnormal if it is easy to accurately obtain the reflected value based upon the detected vehicle wheel speed.
As described earlier, there are cases in which, the reflected value of the vehicle wheel cannot be accurately obtained when the tire condition amount (for example, tire pressure and the like) is normal. Reversing this causal relationship, it follows that if the reflected value of the vehicle wheel can be accurately obtained, then there is a high probability that the tire condition amount of that vehicle wheel is abnormal.
Based upon such knowledge, if the reflected value is difficult to accurately obtain based upon the detected vehicle wheel speed, then it is determined that there is a high probability that the tire condition amount of the vehicle wheel is normal, and if the reflected value is easy to accurately obtain, then it is determined that there is a high probability that the tire condition amount of the vehicle wheel is abnormal.
The determination whether accurately obtaining the reflected value based upon the detected vehicle wheel speed is difficult can generally be conducted with relative ease and in a short time.
Therefore, according to this apparatus, it becomes relatively easy and simple to make the determination whether there is a high probability that the tire condition amount of the vehicle wheel is abnormal in a short time.
In the case where the tire vibration resonance frequency is obtained as the reflected value based upon the vehicle speed, a phenomenon in which time-dependent fluctuations of the obtained resonance frequency are equal to or above a setting state arises due to the fact that the tire vibration frequency characteristic reflected by the vehicle wheel speed is not sufficiently peaked at the position of that resonance frequency, i.e. a resonance phenomenon does not conspicuously occur, signifying the possibility of a resulting difficulty in accurately obtaining the reflected value.
A third aspect of the invention relates to an apparatus for estimating a tire condition amount of that vehicle wheel provided in a vehicle equipped with first and second vehicle wheels, each formed with air enclosed under pressure in an inside portion of a tire mounted to a disc wheel. This apparatus includes a first wheel speed sensor that detects a first vehicle wheel speed of the first vehicle wheel and that is provided in relation to the first vehicle wheel; a second wheel speed sensor that detects a second vehicle wheel speed of the second vehicle wheel and that is provided in relation to each of the second vehicle wheel; and an estimating unit. The estimating unit obtains a reflected value reflecting a tire condition amount of the second vehicle wheel for which it is relatively easy to accurately obtain the reflected value of the second vehicle wheel based upon the detected second vehicle wheel speed, relative to the first vehicle wheel, during a first period corresponding to a second period in which it is relatively difficult to obtain a reflected value reflecting a tire condition amount of the first vehicle wheel based upon the first vehicle wheel speed, and estimates the reflected value of the first vehicle wheel based on the obtained reflected value of the second vehicle wheel, and estimates the tire condition amount of the first vehicle wheel based upon the estimated reflected value of the first vehicle wheel.
According to the third aspect, the tire condition amount of the first vehicle wheel can be obtained based on the obtained reflected value of the second vehicle wheel during the first period corresponding to the second period in which it is relatively difficult to obtain the reflected value of the first vehicle.
A fourth aspect of the invention relates to a method that estimates a tire condition amount of a vehicle wheel formed with air enclosed under pressure in an inside portion of a tire mounted to a disc wheels. The method includes the steps of detecting a vehicle wheel speed of each of a plurality of vehicle wheel, obtaining a reflected value reflecting a tire condition amount of each of the plurality of vehicle wheels based on the detected vehicle wheel speed corresponding to each of the plurality of vehicle wheels, estimating a reflected value of a first vehicle wheel for which it is relatively difficult to accurately obtain the reflected value based upon a vehicle wheel speed of the first vehicle wheel among the plurality of vehicle wheels, during a first period corresponding to a second period for obtaining the reflected value of the first vehicle wheel, based upon a reflected value obtained for a second vehicle wheel for which it is relatively easy to accurately obtain the reflected value based upon a vehicle wheel speed of the second vehicle wheel in order to obtain the reflected value of the first vehicle wheel, and estimating the tire condition amount based upon the obtained reflected value.
A fifth aspect of the invention relates to a method that estimates a tire condition amount of a vehicle wheel formed with air enclosed under pressure in an inside portion of a tire mounted to a disc wheel. The method includes the steps of detecting a vehicle wheel speed of the vehicle wheel, obtaining a reflected value reflecting a tire condition amount of the vehicle wheel based upon the detected vehicle wheel speed, estimating the tire condition amount based upon the obtained reflected value, and determining that there is a high probability that the tire condition amount of the vehicle wheel is normal if it is relatively difficult to accurately obtain the reflected value based upon the detected vehicle wheel speed, and determining that there is a high probability that the tire condition amount of the vehicle wheel is abnormal if it is relatively easy to accurately obtain the reflected value based upon the detected vehicle wheel speed.
A sixth aspect of the invention relates to a method for estimating a tire condition amount of a vehicle wheel formed with air enclosed under pressure in an inside portion of a tire mounted on a disc wheel. This method includes the steps of detecting a first vehicle wheel speed of the first vehicle wheel; detecting a second vehicle wheel speed of the second vehicle wheel; obtaining a reflected value reflecting a tire condition amount of the second vehicle wheel for which it is relatively easy to accurately obtain the reflected value of the second vehicle wheel based upon the detected second vehicle wheel speed, relative to the first vehicle wheel, during a first period corresponding to a second period in which it is relatively difficult to obtain a reflected value reflecting a tire condition amount of the first vehicle wheel based upon the first vehicle wheel speed; estimating the reflected value of the first vehicle wheel based on the obtained reflected value of the second vehicle wheel; and estimating the tire condition amount of the first vehicle wheel based upon the estimated reflected value of the first vehicle wheel.